1. Field of the Invention
The present invention relates to an electrostatic copying apparatus in which an electrostatic image formed on the surface of a photosensitive member and corresponding to an original document is developed by a developing material into a visible toner image for subsequent transfer thereof onto a transfer paper or copying paper, and more particularly to a transfer type electrostatic photographic copying apparatus equipped with a charge eraser lamp disposed posterior to the transfer process for removal of residual charge remaining on the photosensitive member.
2. Description of the Prior Art
In the conventional transfer type electrostatic copying apparatus, organic photoconductive material is used as the photosensitive medium or photoreceptor on which the electrostatic latent image is to be formed, and for developing such electrostatic latent image formed on the photosensitive member, two component developing material which is a mixture of carrier and toner with a high electrical insulation has been employed. The organic photoconductive material which is inexpensive, highly sensitive, easy to manufacture and further flexible has such advantages that it can be formed not only into a drum shape, but also into a belt-like configuration for use, and therefore, it has come to be widely employed as a photosensitive member for electrophotography in spite of its physical and chemical unstability as compared with inorganic photoconductive materials.
Accordingly, when the two-component developing material is to be employed, it is necessary to maintain the mixing ratio of the carrier and toner constant at all times, while due to the limited life of the carrier, it is also required to periodically exchange the developing material in the developing device, and thus, the two-component developing material cannot be said to be easy to maintain, with a further problem that the size of the developing device is comparatively increased. Different from the two-component developing material as described above, one-component developing material containing no carrier is superior in that it is free from the above-mentioned problems and has the possibility of wide application in the future.
Accordingly to experiments carried out by the present inventors, it is found that, in a transfer type electrostatic copying apparatus which employs a photosensitive member made of the organic photoconductive material and the one-component developing material, a new phenomenon takes place in which the density of the copied images is reduced upon repetition many times of the copying operation. The reduction of the image density as described above is a phenomenon previously unnoticed and is different from the conventionally-known fatigue phenomenon of the photosensitive member, and thus, it is made clear that, unless such a new phenomenon is eliminated, the transfer type electrostatic copying apparatus utilizing a photosensitive member of organic photoconductive material and one-component developing material will be difficult to be brought into actual use.
In brief, therefore, a prior art transfer type electrostatic copying apparatus employing a photosensitive member made of organic photoconductive material and the one-component developing material has suffered from reduction of density and lower quality of the copied image.